There is a growing interest in ICP's with good paint adhesion properties, in particular in the automotive industry for items such as bumper fascia. These materials must have mechanical properties appropriate to their use, such as high flexural modulus, high Izod impact energy, sufficient low-temperature impact energy and ductility, and acceptable elongation at break. They often must also be paintable in order to ensure a pleasing appearance of the entire product incorporating them. In the case of an automobile bumper, for example, the bumper and the rest of the car's exterior must be matched in color. “Paintable” in this context means that paint must adhere well to the polymer.
Paintability and mechanical properties tend to be in opposition: those compositional properties that tend to make an ICP paintable do not usually tend to give it desirable mechanical properties, and vice-versa. For example, a relatively high concentration of amorphous ethylene-propylene rubber having a low intrinsic viscosity is believed to enhance paintability but reduce stiffness. The present invention includes an impact copolymer composition and method for making the composition. Articles molded using the composition achieve a good balance between the requirements of paintability and mechanical properties.